Continuing the discussion about noinput / anyprevout

The discussion revolves around the implementation of Decker-Russell-Osuntokun (DRO) and eltoo, two off-chain payment channel constructions for Bitcoin's Lightning Network. The focus is on the use of trigger transactions to separate timeout start and the actual update/settlement pairs in eltoo, which does not require a pre-signed settlement transaction. The first update and settlement pair can be signed without noinput/anyprevoutanyscript, enabling output tagging, but mandates that unilateral closes must publish the first update as well. While it is desirable to keep outputs unidentifiable, the existence of unpublished channels in Lightning networks means that we selectively tell others about the channel's existence, reducing network noise and adding uncertainty for attackers trying to profile nodes. Historical channels that have been cooperatively closed are no longer gossiped, so the fact that they used to be channels is no longer widely broadcast, necessitating that anyone who wants to record historical use of Lightning retain the information themselves.